(1.) Field of the Invention
This invention relates to a one-way clutch and more specifically to a one-way clutch with a cage-displacement limiting mechanism.
(2.) Description of the Prior Art
Typical conventional one-way clutches (hereinafter called "OWC") are sprag-type OWCs equipped with double cages, namely, both inner and outer cages. In a sprag-type OWC, the inner and outer cages serve to arrange plural sprags with equal angular intervals and to have all the sprags move in unison. The structures and functions of conventional sprag-type OWCs will hereinafter be described in brief with reference to FIGS. 9 and 10.
FIG. 9 is a fragmentary cross-sectional view of a sprag-type OWC having double cages. A flange 5a of an outer cage 5 is guided by an inner peripheral surface 1a of an outer race 1, while a flange 7a of an inner cage 7 is guided by an outer peripheral surface 3a of the inner race 3. All sprags 11 can be brought into simultaneous engagement with the outer cage 5 and inner cage 7 to bear each torque evenly, because the sprags 11 are allowed to move relative to movements of the outer and inner races 1,3. In the illustrated example, a ribbon spring 9 is interposed between the outer and inner cages 5,7 so that the sprags 11 are normally maintained in contact with the inner and outer peripheral surfaces 1a,3a. In FIG. 10, the flange 5a of the outer cage 5 is positioned at a stepped portion of the outer race 1, where the flange 5a is supported by a support member 13. Further, the flange 7a of the inner cage 7 extends toward the inner peripheral surface 1a of the outer race 1.
In the above-described conventional sprag-type OWCs each of which is equipped with the double cages, the so-called full phasing effect is known to take place when the sprags are moved from their free positions to their torque-transmitting locked positions. It is hence possible to achieve smooth transmission of torques even somewhat severe use conditions.
The above-described prior art is however accompanied by various problems. When such a conventional OWC is subjected to an excess torque, its sprags are caused to rise from their normal free positions and then to fall in the opposite direction beyond the cam height, in other words, to undergo the so-called rollover. As secondary outcomes, the cages are deformed or broken and the ribbon spring are caused to undergo fatigue due to its deformation. In addition, deep impressions are formed in both inner and outer races, thereby making them no longer usable. In some severe instances, the sprags cut into the outer and inner peripheral surfaces of the inner and outer races and are no longer allowed to idle.
If the sprags undergo slipping and are hence unloaded while they are maintained in engagement with the outer and inner peripheral surfaces of the inner and outer races, the sprags are immediately caused to fall toward the free side as a counteraction to the release of the load, in other words, the so-called popping phenomenon develops. The sprags thus start stepping and hopping in a very short period of time. As a result, the sprags collide severely against the inter-pocket parts of the cages and the cages are hence worn and deformed. In some worst cases, the sprags may move beyond their associated inter-pocket parts and enter forcibly between both cages. This phenomenon is called "pop-out". When the sprags undergo popping, skid marks are formed on the inner cam surfaces of the sprags and the inner cam surfaces are therefore worn out, leading to wearing and breakage of the interpocket parts of the cages, deformation and breakage of the ribbon spring, etc. Even if only one of the sprags pops out, the inner cage is turned toward the idling side by the pop-out and the other sprags are hence tilted toward the free side and are thus separated from the outer peripheral surface of the inner race. As a consequence, the OWC loses its function as an OWC and can no longer transmit torques.
As typified by the above-described two examples, it is the falling of sprags that causes serious problems in sprag-type OWCs. An OWC cannot function properly when its sprags fall excessively not only toward the free side but also toward locked side.
In order to solve the above-described problems, it is indispensable to perform very strictly the control of the designing of the outer configurations of the sprags including their strut angles and the control of the dimensional accuracy of the pockets of the inner cage. It may also be contemplated to increase the thickness of the inner cage and/or the torque capacity of the OWC so as to increase the safety factor. It may also be necessary to improve the material of the ribbon spring so as to make it more flexible.
If one tries to solve the above problems in the aforementioned manner, secondary problems arise such that the device becomes more complex in that its manufacturing cost increases substantially due to the need for strict designing and control of the dimensions of various parts, and the assembly work becomes difficult. Therefore, the above-mentioned solution cannot be fully considered as a breakthrough and practical solution.